Obese children choose to be sedentary rather than active, and sedentary behaviors influence weight control since they compete with being active, and set the occasion for excess caloric intake. We recently demonstrated that reinforcing children for reducing sedentary behaviors resulted in superior weight control compared to children who were reinforced for being active, or reinforced for the combination of increasing active and reducing sedentary behaviors. All children showed similar improvements in fitness. Preference for being active was increased the most for children who were reinforced for reducing their sedentary behavior. These results suggest the relevance of targeting sedentary behaviors to improve childhood weight control. The proposed clinical and laboratory studies are designed to understand factors that influence the choice of sedentary versus active alternatives. The clinical outcome study assesses the parameters of the changes in sedentary or active behaviors associated with superior weight control observed when a decrease in sedentary behaviors rather than an increase in active behaviors is reinforced. Obese children will be randomized to one of four groups who are provided our standard family- based behavioral treatment program, varying the amount of leisure time sedentary behaviors allowed or the amount of exercise prescribed. Activity patterns, activity preference, intake, laboratory assessment of the relative reinforcing value of vigorous or sedentary activity and measures of decisional balance and perception of choice will be measured to understand how these variables influence weight change. The three laboratory studies provide direct tests of mechanisms for the clinical phenomena we have identified. The first study tests the importance of reinforcing a decrease in sedentary behaviors versus an increase in active behaviors; the second study tests the importance of targeting high or low preference sedentary behaviors; and the third study tests three alternative ways to decrease sedentary behavior. In each study free choice for active or sedentary alternatives will be assessed before and after multiple days in which the experimental procedures have been in effect.